1. Field of the Invention
This invention relates to disk drives and disk control circuits that identify the boundaries of headerless data sectors.
2. Description of Related Art
A conventional magnetic media for a hard drive is a disk having major surfaces divided into concentric tracks for data storage. Servo wedges, which are spaced about the disk in a spoke-like pattern, subdivide the tracks into data frames. The portion of a servo wedge within a track is referred to as a servo sector and separates one data frame in the track from another. Typically, a servo sequencer uses the servo sectors in a track to keep a data head following the track and generates end-of-servo (EOS) pulses marking the ends of servo sectors and the beginnings of data frames. In addition to track following information, a servo sector often contains an ID field identifying the servo sector and an associated data frame.
Data in data frames is typically organized into data sectors, each of which contains the same amount of data, for example, 512 bytes. The data sectors may include a single data segment that is entirely within a data frame or multiple data segments that are separated from each other, for example, by a servo sector. For constant density recording, the disk area per data byte is constant, but the amount of data that fits within a data frame varies because the available area depends on the circumferences of the track containing the data frame. Accordingly, the locations of boundaries (i.e. the starts and splits) of data sectors depend on the track.
When reading or writing a data sector, the boundaries of each data segment need to be identified. One method for identifying data sector boundaries uses information from a header of a data sector to locate splits in the data sector. However, split information stored in headers wastes disk space that could otherwise store data.
A headerless data sectors lacks headers containing split information which leaves more disk area for data storage. However, a disk sequencer still requires split information to locate the boundaries of data sectors and segments. A hard disk can store such split information in non-volatile memory, on disk in data sectors, or in a data buffer memory. The split information typically takes the form of look-up tables that describe track formats. For example, a hard disk would typically require one look-up table per zone of tracks having a common track format. Each table contains format words associated with particular data frames, data sectors, or data segments. If, for example, a hard disk having 20 different zones of tracks and 64 embedded servo wedges requires an average of three words of split information per data frame, the hard disk requires twenty look-up tables and a total of 3840 words of split information.
To avoid degrading performance, a hard disk commonly requires additional data buffer capacity, bandwidth, and processing power for handling the split information. If the required bandwidth is not available when required to transfer split information to a disk sequencer, the hard disk may miss a data sector and delay a transfer for a revolution of the disks. Additionally, firmware executed by a microprocessor in the disk drive must identify the table and split information that corresponds to the current position of the data heads relative to a track being followed. The calculations required to identify the split information can be complex and consume processing power that could otherwise be used for other purposes such as controlling a servo sequencer, managing a data buffer, handling a host interface, and converting read/write requests to a list of physical data sector to be accessed. Processes and/or circuits are sought that reduce the amount of split information and reduce the processing demands on a microprocessor in a hard drive.